Quality control of the micro-ELISA technic applied to the diagnosis of human and canine visceral leishmaniasis.

Abstract

Visceral leishmaniasis (VL) or kala-azar is, in Portugal, a zoonosis with the dog as reservoir. A quality control of the technique of micro-ELISA was carried out, using as reference the technique of IFI, the most commonly used for the diagnosis of this protozoosis, both for human and canine sera. Three different methods were used to estimate the cut-off point: X + 2sd (average for negative sera plus two standard deviation), P/N and J index. As quality parameteres were used sensitivity, specificity, efficacy and positive predictive value. The cut-off point for human sera was established at 0.100 A, with 100% sensitivity, 90.5% specificity, 95.3% efficacy and 91.4% positive predictive value, and for canine sera in 0.200 A, with 80.0% sensitivity, 94.3% specificity, 87.7% efficacy and 96.6% positive predictive value. Reproducibility was not fully satisfactory and two different ways of improving it are proposed: P/N and a correction factor. A statistically significant correlation was observed between micro-ELISA's absorbances and IFI titres regarding human sera, though it was not possible to do the same for dog sera.